Changes in Weight Over Time Can Determine Risk of Type 2 Diabetes

Changes in weight and diabetes risk: weight loss between young adulthood and midlife found to create statistically significant reductions in risk for diabetes.

Adults with obesity who shed pounds and dropped down to a non-obese body mass index (BMI) before hitting middle age dramatically reduced their risk for diabetes, according to a retrospective cohort study.

These individuals lowered their risk by nearly 70% (hazard ratio 0.33; 95% CI 0.14-0.76) compared with those who had obesity as young adults and stayed that way in middle age, researchers led by Andrew Stokes, PhD, of the Boston University School of Public Health, reported in Diabetes Care.

Understanding how changes in weight over the life course shape risk for diabetes is critical for the prevention of diabetes. Using data from the National Health and Nutrition Examination Survey (NHANES), researchers investigated the association between self-reported weight change from young adulthood to midlife and incident diabetes.

The incidence and prevalence of diabetes among adults in the U.S. has risen during the past 30 years. In 1988, 9.8% of the adult population was living with diabetes; by 2014, this prevalence had grown to 12.3%. These increases have important implications for U.S. mortality, morbidity, disability, and health care expenditures.

A recent study found that diabetes was responsible for a higher volume of personal medical expenditures than any other medical condition. A 2017 study estimated that nearly one-fifth of deaths among obese adults were attributable to diabetes. A rising trend in the prevalence of obesity can account for most of the increase in diabetes between 1976 and 1980 and between 2007 and 2010. The relationship between obesity and diabetes has been established by observational studies of BMI and diabetes status, and supported further by research into the physiologic link between body fat, insulin resistance, and type 2 diabetes. Alongside the effects of prevalent obesity on diabetes, prospective cohort studies have shown weight change over the life course can also have profound effects on the risk of diabetes.

A recent study using data from the Nurses’ Health Study and the Health Professionals Follow-up Study examined major health outcomes associated with weight change in adulthood. Of the outcomes considered, type 2 diabetes showed the strongest associations with weight change. A general reduction in risk was observed for weight loss in both cohorts, whereas weight gain was associated with an increased incidence of diabetes commensurate with the absolute change. These associations have also been observed in studies outside the U.S. and in studies focused on ethnic differences.

NHANES has routinely asked questions about weight histories, including weight at age 25 and weight 10 years before the survey, alongside weight at the survey. It has also asked questions about the history of diabetes diagnosis. Leveraging these data provides an opportunity to investigate the relationship between weight histories, in the form of weight at age 25 and weight 10 years before the survey, and the incidence of diabetes during 10 years of follow-up before the survey. They used this approach to examine the relationship between weight change in adulthood and diabetes incidence and sought to determine whether obese individuals who lost weight were at a reduced risk of diabetes relative to individuals with stable obesity, and at an increased risk of diabetes relative to individuals who maintained a nonobese BMI over time.

The researchers categorized individuals into four weight-change groups: those who remained nonobese (stable nonobese), those who moved from an obese BMI to a nonobese BMI (losing), those who moved from a nonobese BMI to an obese BMI (gaining), and those who remained obese (stable obese). Diabetes status was determined by self-report of a prior diagnosis, and age at diagnosis was used to establish time of diabetes onset. Hazard ratios (HRs) relating weight change to incident diabetes over 10 years of follow-up were calculated using Cox models adjusting for covariates.

The results are consistent with other evidence based on nonnational sources that duration of obesity predicts the incidence of diabetes.

However, the 95% CIs were wide because weight loss from an obese BMI to a nonobese BMI was rare, representing only 1.1% of the total population. They used estimates of the risks associated with weight change to explore the potential effect of weight loss interventions and prevention initiatives targeting weight gain. The weight loss scenario was designed to approximate a comprehensive weight loss intervention targeting individuals with obesity at age 25. They estimated that if all those who were obese at age 25 lost to a nonobese BMI by midlife, 9.1% (95% CI 5.3, 12.8) of observed incident cases of diabetes could be averted. Preventing weight gain in the population after age 25, represented by the weight maintenance scenario, was associated with a 23.5% (95% CI 21.8, 25.1) reduction in diabetes cases in the population.

In total, they found that 64.2% (95% CI 59.4, 68.3) of diabetes cases during this time period could be averted if all individuals in the population maintained a weight in the normal range between early adulthood and midlife.

The findings from this study underscore the importance of population-level approaches to the prevention and treatment of obesity across the life course of individuals.

Practice Pearls:

It was found that those who lost weight between young adulthood and midlife showed statistically significant reductions in risk for diabetes onset compared with those who remained obese.

The category with the highest risk of incident diabetes consisted of people who had obesity during both young adulthood and midlife.

Not having obesity at age 25 or 10 years before the survey was advantageous relative to remaining without obesity throughout this period.